1. Field of the Invention
This invention relates to freeze protection devices and more particularly to a valve assembly which is automatically responsive to ambient temperatures at the freezing point of water, whereby damage to aqueous systems caused by freezing of water in pipes can be automatically prevented without reliance upon external sources of power.
2. Review of the Prior Art
Power failures during blizzards in northerly climates can cause severe freezing damage to pipes and water damage to the interiors of unoccupied homes during a subsequent thaw. Such freezing can occur in both water supply systems and hot water and steam heating systems. In addition, freezing of water in pipes, causing rupture of the pipes and subsequent damage to buildings by melted water, is a common difficulty in areas of the world where severe freezing is sufficiently infrequent that plumbing design does not include complete thermal protection. Such freezing is by no means limited to exposed faucets and can occur in any unprotected water pipe when ambient temperatures drop to 32.degree. F. and below. Manually opening an exposed valve, to allow steady dripping from a water supply system at the onset of potentially freezing weather, is commonly done to prevent such damage. However, it is necessary that a householder be aware of an oncoming freezing period and remember to open and close the valve. Moreover, if the householder is away from home when the freezing occurs, or if the home is a vacation home in an area where freezing is normally unexpected, such manual opening for freeze protection may be unavailable.
Many freeze protection devices have been developed, but they generally require an external power source, use complicated springs or bellows devices, or rely upon o-rings or other sealing means which are susceptible to undisclosed failure.
U.S. Pat. No. 3,369,556 of Allderdice describes a freeze protection valve for water supply systems. The valve has a single bellows filled with water which expands when it freezes to move a valve element off its seat against the water pressure within a water line. This valve must be mounted vertically so that bypass water passes upwardly through the device to be discharged. This freeze device requires a loss motion adjustment for its bellows system to permit free expansion and contraction of the water contained therein.
U.S. Pat. No. 3,380,464 of Arterbury, et al describes a temperature-responsive valve adapted to be installed in a water line to protect it against freezing by opening a bleed actuator which comprises an elongated housing surrounding an annular expansion chamber and an axially disposed valve member which is hollowed to allow bypass water to flow through and be discharged from the valve member while heating the inner wall of the expansion chamber. To enhance such heat transfer, a portion of the valve member extends into the water line. After the valve has been opened to bleed water from the water line, it thereafter closes because of such heat transfer and is again in position to operate responsively to freezing ambient temperatures. The valve thereby utilizes the concept of heat balance between heat supplied by the flowing water and heat lost to the atmosphere.
U.S. Pat. No. 3,618,625 of Walters is directed to preventing freezing of water within a watering tank for animals which is connected to a pressurized source of warmer water. The tank has an inflow inlet conduit and a valve device which regulates outflow. This valve device comprises a sensing bulb connected to one end of a tubular conduit which is connected at its other end to a bellows and an outflow tube having a valve heat surface. When freezing temperatures are sensed by the bulb, there is an outflow of water from the valve device and an inflow of water from the inlet conduit, thereby preventing freezing of water within the tank.
U.S. Pat. No. 4,638,828 of Barrineau, Sr., et al. discloses an automatically operated valve to prevent freezing of water lines. The water faucet has female threads to accommodate a drip valve which is threaded into a standard "tee" type plumbing fitting. The drip valve includes an elongated housing having a temperature monitoring device within its upper end and a moveable tip at its lower end. When water temperature falls to freezing levels, a wax-like substance in the upper portion of the device contracts, causing the tip to reflex and allow water to flow through an opening at the bottom of the device.
The TL ambient sensing control valve for steam tracing systems and the Type F and Type AF valves for water systems, both sold by the Ogontz Controls Co., 141 Terwood Road, P.O. Box 479, Willow Grove, Pa. 19090, utilize an operating spring and an overtemperature spring. An externally disposed thermal actuator, filled with a solid-liquid phase wax, is on one end of the valve yoke which is connected to these springs and has a silicone plug on its other end for engaging the valve seat. These devices can be set for operation at a selected temperature.
None of the prior art devices can be considered safe from mechanical failure before onset of freezing weather. Devices requiring adjustment to set the temperature of actuation are subject to wrong settings or to change of settings caused by movement in the mechanism. Other devices containing an actuation chamber filled with water or another expansible substance can be subject to undetected leakage through o-rings, seals, or threads, and consequently will fail to open during sub-freezing conditions. If such failure occurs, the condition will not be visible in these devices until after the freeze has been followed by a thaw.
Still other devices depend upon an outside source of power for actuation. If there is a power failure, the device will fail to operate, and freeze damage will occur.
Moreover, industrial factories and chemical plants in many parts of the world have numerous pipelines and equipment containing water that are protected from freezing by heating with steam. The steam is used to heat the water by direct injection of steam into the water or by indirect heating of the water by using coils containing steam in direct contact with water, such as a coil of tubing or a plate coil submerged in a water tank, or by using coils containing steam in contact with the wall of the system containing the water. Examples of such indirect contact are: tubing (usually copper) containing steam strapped to a water pipeline, tubing containing steam wrapped around a tank, and a steam-plate coil containing steam strapped to a tank containing water.
In most instances, the system containing the steam and the system containing water are both wrapped with insulation. Systems containing water may include water lines, return steam lines, and aqueous solution lines. Such lines may be hundreds of feet long, and rupture thereof during freezing weather, as can occur during a power failure, can cause shutdown of an entire plant.
Thus, there is a need for a completely failure-safe freeze prevention valve that is useful under industrial conditions, automatically responsive to freezing temperatures and to thawing temperatures, completely reliable as a standby device, entirely independent of outside power sources, incapable of leaking, and operable without periodic maintenance.
Furthermore, in those parts of the country in which pipelines and equipment are subjected to sub-freezing conditions, the steam used for protecting water systems in most industrial plants is turned on manually in the fall of the year, before a freeze occurs, and is turned off manually in the spring, after the last freeze. This practice is particularly prevalent for water lines that are steam traced and insulated. It results in a loss of steam energy while the steam system is on during ambient temperatures that are above freezing.
There is, accordingly, a need for a failure-safe freeze prevention valve for industrial plants that is automatically operable during freezing weather and is automatically inoperable under other weather conditions without manual or electrical operation thereof.